Button cells and method of producing same

ABSTRACT

A method for producing a button cell includes providing a cell cup, a cell top and an electrode-separator assembly winding, the electrode-separator assembly winding having a positive electrode and a negative electrode. An electrically insulating seal is applied at least to an outer portion of the cell top casing. The electrode-separator assembly winding is inserted into the cell top. The cell top is inserted into the cell cup to form a housing. A pressure is applied in a radial direction perpendicular to an axis of the electrode-separator assembly winding so as to seal the housing.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This is a divisional of U.S. Ser. No. 15/696,354, filed Sep. 6, 2017,which is a divisional of U.S. Ser. No. 15/283,568, filed Oct. 3, 2016,which is a continuation of U.S. Ser. No. 14/827,387, filed Aug. 17,2015, which is a divisional of U.S. Ser. No. 13/146,669, filed Sep. 7,2011, which is a § 371 of International Application No.PCT/EP2010/000787, with an international filing date of Feb. 9, 2010 (WO2010/089152 A1, published Aug. 12, 2010), which claims priority toGerman Patent Application Nos. 10 2009 008 859.8, filed Feb. 9, 2009, 102009 030 359.6, filed Jun. 18, 2009, and 10 2009 060 788.9, filed Dec.22, 2009, all of which above applications are hereby incorporated byreference herein.

FIELD

This disclosure relates to button cells comprising two metallic housinghalf-parts separated from one another by an electrically insulating sealand which form a housing with a flat bottom area and a flat top areaparallel to it, as well as within the housing, an electrode-separatorassembly comprising at least one positive and at least one negativeelectrode, which are in the form of flat layers and are connected to oneanother by at least one flat separator, and to a method of producingsuch button cells.

BACKGROUND

Button cells normally have a housing consisting of two housinghalf-parts, a cell cup and a cell top. By way of example, these may beproduced from nickel-plated deep-drawn metal sheet as stamped and drawnparts. The cell cup normally has positive polarity, and the housing topnegative polarity. The housing may contain widely differingelectrochemical systems, for example, zinc/MnO₂, primary and secondarylithium systems, or secondary systems such as nickel/cadmium ornickel/metal hydride.

By way of example, rechargeable button cells based on nickel/metalhydride or lithium-ion systems are in widespread use. In the case oflithium-ion button cells, the electrochemically active materials arenormally not arranged within the button cell housing in the form ofindividual electrodes, in the form of tablets, separated from oneanother by a separator. Instead, prefabricated electrode-separatorassemblies are preferably inserted flat into the housing. In that case,a porous plastic film is preferably used as a separator, onto which theelectrodes are laminated or adhesively bonded flat. The entire assemblycomprising the separator and the electrodes generally have a maximumthickness of a few hundred μm. To allow button cell housings of normaldimensions to be filled, a plurality of such assemblies are thereforefrequently placed flat one on top of the other. This allows stacks ofany desired height, in principle, to be produced, in each case matchedto the available dimensions of the button cell housing into which thestack is intended to be installed. This ensures optimum utilization ofthe available area within the housing.

By virtue of the design, however, various problems also occur in thecase of button cells which contain such stacks of electrode-separatorassemblies. On the one hand, it is necessary, of course, for theelectrodes of the same polarity each to be connected to one anotherwithin the stack, and then each to make contact with the correspondingpole of the button cell housing. The required electrical contacts resultin material costs, and the space occupied by them is, furthermore, nolonger available for active material. In addition, the production of theelectrode stacks is complicated and expensive since faults can easilyoccur when the assemblies make contact with one another, increasing thescrap rate. On the other hand, it has been found that button cellshaving a stack of electrodes and separators very quickly start to leak.

Traditionally, button cells have been closed in a liquid-tight manner bybeading the edge of the cell cup over the edge of the cell top inconjunction with a plastic ring, which is arranged between the cell cupand the cell top and at the same time acts as a sealing element and forelectrical insulation of the cell cup and of the cell top. Button cellssuch as these are described, for example, in DE 31 13 309.

However, alternatively, it is also possible to manufacture button cellsin which the cell cup and the cell top are held together in the axialdirection exclusively by a force-fitting connection, and which do nothave a beaded-over cup edge. Button cells such as these and methods fortheir production are described in German Patent Application 10 2009 017514. Irrespective of the various advantages which button cells such asthese without beading may have, they can, however, not be loaded asheavily in the axial direction as comparable button cells with abeaded-over cup edge, in particular with respect to axial mechanicalloads which are caused in the interior of the button cell. For example,the electrodes of rechargeable lithium-ion systems are continuallysubject to volume changes during charging and discharging processes. Theaxial forces which occur in this case can, of course, lead to leaks morereadily in the case of button cells without beading than in the case ofbutton cells with beading.

It could therefore be helpful to provide a button cell in which theproblems mentioned above do not occur, or occur only to a greatlyreduced extent. In particular, it could be helpful to provide a buttoncell that is resistant to mechanical loads which occur in the axialdirection than conventional button cells, in particular even when theyare manufactured as button cells without a beaded-over cup edge.

SUMMARY

The present invention provides a method for producing a button cell,including: providing a cell cup, the cell cup having a flat bottom area,a cell cup casing, and a bottom edge forming a transition between theflat bottom area and the cell cup casing; providing a cell top, the celltop having a flat top area, a cell top casing having a first height, anda top edge forming a transition between the flat top area and the celltop casing, wherein at least a portion of the cell top casing iscylindrical; providing an electrode-separator assembly winding, theelectrode-separator assembly winding having a positive electrode and anegative electrode in the form of layers connected to one another by aseparator layer and wound up in a spiral shape about an axis, wherein afirst of the positive electrode and the negative electrode is formedfrom a first metallic film or metallic mesh covered with an electrodematerial, the first metallic film or metallic mesh including anuncovered end piece; applying an electrically insulating seal at leastto an outer portion of the cell top casing; inserting theelectrode-separator assembly winding into the cell top; inserting thecell top into the cell cup to form a housing, wherein: the flat top areais parallel to the flat bottom area, the axis of the electrode-separatorassembly winding is aligned at right angles to both the flat top areaand the flat bottom area, the first metallic film or metallic mesh isbent such that at least a portion of the uncovered end piece extends outof the electrode-separator assembly winding and at least partially liesflat between an end face of the electrode-separator assembly winding andone of the flat bottom area or the flat top area, and the cell topcasing and the cell cup casing form an overlap area extending in adirection parallel to the axis of the electrode-separator assemblywinding and having a second height, the second height being between 20%and 99% of the first height; and applying, in a radial directionperpendicular to the axis of the electrode-separator assembly winding, apressure on the cell cup casing so as to seal the housing, wherein theportion of the cell top casing that is cylindrical forms at least a partof the overlap area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the cross section through one preferredexample of a button cell.

FIG. 2 illustrates the effect of heat treatment of a wound-upelectrode-separator assembly, which is used in preferred examples of ourmethod.

FIGS. 3 a and 3 b show electrode-separator assemblies in the form of awinding, as can be installed in a button cell.

FIG. 4 shows a section illustration of a further preferred example of abutton cell.

FIG. 5 schematically illustrates the cross section through one preferredexample of a button cell in which the edge of the cell cup is not beadedover the edge of the cell cop.

FIG. 6 shows an electrode-separator assembly in the form of a winding,as can be installed in a button cell.

DETAILED DESCRIPTION

In an embodiment, our button cell comprises two metallic housinghalf-parts separated from one another by an electrically insulating sealand form a housing with a flat bottom area and a flat top area parallelto it. As already mentioned initially, the two housing half-parts aregenerally a so-called “housing cup” and a “housing top.” In particular,parts composed of nickel-plated steel or metal sheet are preferred ashousing half-parts. Furthermore, trimetals, for example, with thesequence of nickel, steel (or stainless steel) and copper (with thenickel layer preferably forming the outer layer and the copper layerpreferably forming the inside of the button cell housing) areparticularly suitable for use as the metallic material.

By way of example, an injection-molded or film seal can be used as aseal. The latter are described, for example, in DE 196 47 593.

Within the housing, a button cell comprises an electric-separatorassembly with at least one positive and at least one negative electrode.These are each in the form of flat electrode layers. The electrodes areconnected to one another via a flat separator. The electrodes arepreferably laminated or adhesively bonded onto this separator. Theelectrodes and the separator generally each have thicknesses only in theμm range. In general, a porous plastic film is used as the separator.

In contrast to the button cells mentioned above, our button cell isdistinguished in particular by the electrode layers having a veryparticular orientation, specifically being aligned essentially at rightangles to the flat bottom and top areas. While known button cells withstacked electrode-separator assemblies always contain these assembliesinserted flat such that the electrode layers are aligned essentiallyparallel to the flat bottom and top areas, the situation in our buttoncell is the opposite of this.

The right-angled alignment of the electrode layers has an unexpectedlyconsiderable advantage, specifically because it has been found that thisalignment results in a considerable improvement in the sealingcharacteristics of our button cell, particularly for button cells basedon lithium-ion systems. The electrodes of rechargeable lithium-ionsystems are continually subject to volume changes during charging anddischarging processes. Volume changes such as these also occur, ofcourse, in the electrodes of our button cell. However, the mechanicalforces created during this process no longer act primarily axially, asin the case of a stack of electrode-separator assemblies which areinserted flat. Because of the right-angled alignment of the electrodes,they in fact act radially. Radial forces can be absorbed very muchbetter than axial forces by the housing of a button cell. The improvedsealing characteristics are presumably a result of this.

Particularly preferably, the electrodes and the flat separator of ourbutton cell are each in the form of strips or ribbons. By way ofexample, the production of our button cell can be based on a separatormaterial in the form of an endless ribbon, onto which the electrodes areapplied, in particular laminated, once again in particular in the formof strips or at least rectangles.

In the housing of our button cell, this assembly is particularlypreferably in the form of a winding, in particular in the form of aspiral winding. Windings such as these can be produced very easily usingknown methods (see, for example, DE 36 38 793), by applying theelectrodes flat, in particular in the form of strips, to a separatorwhich is in the form of an endless ribbon, in particular by laminatingthem on. In this case, the assembly comprising electrodes and separatorsis generally wound onto a so-called “winding mandrel.” Once the windinghas been removed from the winding mandrel an axial cavity remains in thecenter of the winding. This allows the winding to expand into thiscavity, if necessary. However, in some circumstances, this can lead toproblems in making electrical contact between the electrodes and themetallic housing half-parts, and this will be described in more detailin the following text.

The electrode winding is preferably arranged within a button cell (sothat the electrode layers of the winding are aligned at right angles tothe flat bottom area and top area of the housing) such that the endfaces of the winding face in the direction of the flat bottom area andof the flat top area.

Preferably, our button cells have a fixed winding core in the center ofthe winding, which at least partially fills the axial cavity in thecenter of the winding. A winding core such as this fixes the electrodewinding in the radial direction and prevents possible implosion of thewinding into the axial cavity. When the winding expands in this way,this also results in the reduction in the pressure which the end facesof the winding exert in the axial direction, and therefore in thedirection of output conductors which may be arranged there (this isdescribed in more detail further below). If this is prevented, thenthere are generally also no problems with making electrical contactbetween the electrodes and the metallic housing half-parts.

In addition, a winding core such as this also makes the button cell morerobust against external mechanical influences. In general, it is nolonger possible for the electrode winding in the button cell to bedamaged by external mechanical pressure in the axial direction.

Preferably, the electrode winding is a spiral electrode winding, theaxial cavity which has been mentioned in the center of the winding ispreferably essentially cylindrical (in particular circular-cylindrical).On the casing side, it is bounded by the winding, and at the end it isbounded by corresponding surfaces of the bottom area and of the top areaof the button cell housing.

Correspondingly, the winding core which is contained in our button cellis preferably also in the form of a cylinder, in particular a hollowcylinder. The height of a cylinder such as this preferably correspondsto the respective distance between the flat bottom area and the flat toparea, which is parallel to it.

Particularly preferably, the winding core may have radiallyself-expanding characteristics. For example, it is possible for thewinding core to be inserted in a radially compressed configuration intothe axial cavity in the winding of a button cell. When the radiallycompressed winding core expands, it exerts a radial pressure on theelectrode winding surrounding it, thus ensuring a contact pressure inthe axial direction as well.

By way of example, an axially slotted hollow cylinder may be used as aradially self-expanding winding core. However, alternatively, it is alsoconceivable to use other radially self-expanding materials, for example,based on plastic.

Particularly preferably, the winding core is composed of a metal such asstainless steel or plastic.

Particularly preferably, the assembly comprising electrodes and aseparator in our button cell has one of the following layer sequences:

-   -   negative electrode/separator/positive electrode/separator or    -   positive electrode/separator/negative electrode/separator.

Assemblies such as these can be produced and wound very easily withoutshort circuits occurring between electrodes of opposite polarity.

The separators which can be used in our button cell are preferably filmscomposed of at least one plastic, in particular of at least onepolyolefin. By way of example, the at least one polyolefin may bepolyethylene. However, it is also possible to use multilayer separators,for example, separators composed of a sequence of different polyolefinlayers, for example, with the sequencepolyethylene/polypropylene/polyethylene.

It is not essential to use a plurality of separate separators to produceassemblies with the abovementioned sequence. In fact, a separator canalso be looped around the end of one of the electrodes, thus resultingin both sides of this electrode being covered by the separator.

The separators which can preferably be used in our button cellpreferably have a thickness of 3 μm to 100 μm, in particular of 10 μm to50 μm.

The electrodes preferably have a thickness of 10 μm to 1000 μm, inparticular of 30 μm to 500 μm.

Preferably, the negative electrode and the positive electrode in theelectrode-separator assembly are arranged offset with respect to oneanother within the assembly. In this case, an offset arrangement isintended to mean that the electrodes are arranged such that this resultsin a respectively different separation between the electrodes and theflat bottom and top areas in the button cell. In the simplest case, forexample, a positive and a negative electrode can be slightly offset asstrips of the same width applied to the opposite sides of a separatorribbon, as a result of which the distance between the positive electrodeand the upper separator edge is greater than the comparable distancemeasured from the negative electrode. This then applies in the oppositesense, of course, to the distance from the lower separator edge.

Particularly preferably, preferably as a result of this offsetarrangement, the positive electrode, in particular an edge of thepositive electrode, rests directly on the cup part, in particular in theflat bottom area of the cup part, while the negative electrode, inparticular an edge of the negative electrode, rests directly on the toppart, in particular in the flat top area of the top part. In thisexample, a direct electrical and mechanical contact is made between theelectrodes and the cup and top parts. The offset arrangement of theelectrodes with respect to one another therefore makes it possible forthe electrodes to make contact with the respective housing parts,without any need to use additional electrical contacts and connectingmeans.

However, alternatively, it is also preferable for at least one of theelectrodes, preferably both the at least one negative electrode and theat least one positive electrode in our button cell, to be connected tothe flat bottom and top areas via one or more output conductors. By wayof example, the output conductors may be output-conductor lugs composedof copper or some other suitable metal. On the electrode side, theoutput conductors may, for example, be connected to a current collector.The output conductors can be connected to the housing and/or to thecurrent collectors by, for example, welding or via an clamped joint.

In the simplest case, the current collectors of the positive andnegative electrodes can also themselves act as output conductors.Collectors such as these are generally metallic films or meshes whichare embedded in the respective electrode material. Uncovered subareas,in particular end pieces, of collectors such as these can be bent aroundand can be brought into contact with the button cell housing.

The use of output conductors may be particularly advantageous if thenegative electrode and the positive electrode within the assembly arearranged with respect to one another such that this results in theelectrodes each being at the same distance from the flat bottom and topareas. Or, in other words, if the electrodes are not arranged offsetwith respect to one another within the electrode-separator assembly, ashas been described above.

However, if the distance between electrodes of opposite polarity and theflat bottom and top areas is the same, this results in the risk of apositive and a negative electrode touching the metallic cup or top partat the same time, thus resulting in a short circuit. Preferably, thebutton cell may therefore comprise at least one insulating means, whichprevents a direct mechanical and electrical contact between the endfaces of the winding and the flat bottom and top areas.

It is preferable for the electrodes in our button cell such as this tobe connected via the already mentioned separate output conductors to theflat bottom and top areas. These ensure the electrical contact betweenthe electrodes and the housing.

In this case, it is preferable for at least a subsection of the outputconductor or conductors in the bottom area and in the top area of thehousing to rest flat on the inside of the housing half-parts. Ideally,the output conductors naturally make electrical contact with the insidesof the housing when they are at least slightly pressed against thehousing (if they are not welded to it in any case). This can be achievedsurprisingly efficiently by a suitable arrangement of the winding corethat has been mentioned, in our button cell.

By way of example, the insulating means may be a flat layer composed ofplastic, for example, a plastic film, which is arranged between the endfaces of the winding and the flat bottom and top areas of the housing ofour button cell.

Corresponding to the above statements, the button cell is, inparticular, a rechargeable button cell. Our button cell particularlypreferably has at least one lithium-intercalating electrode.

The ratio of the height to the diameter of button cells is, bydefinition, less than 1. For our button cell, this ratio is particularlypreferably 0.1 to 0.9, in particular 0.15 to 0.7. In this case, theheight means the distance between the flat bottom area and the flat toparea parallel to it. The diameter means the maximum distance between twopoints on the casing area of the button cell.

The button cell is particularly preferably a button cell which is notbeaded over, as is described in DE 10 2009 017 514.8, mentioned above.Correspondingly, there is preferably an exclusively force-fittingconnection between the housing half-parts. Therefore, our button celldoes not have a beaded-over cup edge, as is always the case with knownbutton cells. The button cell is closed without being beaded over.

Button cells such as these which are not beaded over generally make useof conventional cell cups and cell tops, which each have a bottom areaand a top area, a casing area, an edge area which is arranged betweenthe bottom and top areas and the casing area, and a cut edge. Together,the cell cup and cell top form a housing, which forms a receptacle forthe conventional internal components of a button cell such aselectrodes, separator and the like. As in the normal way, the bottomarea of the cell cup and the top area of the cell top are alignedessentially parallel to one another in this housing. The casing areas ofthe cell cup and cell top in the finished button cell are alignedessentially at right angles to the bottom and top areas, and preferablyhave an essentially cylindrical geometry. The internal and externalradii of the cell cup and cell top are preferably essentially constantin the casing areas. The edge areas, which have been mentioned, of thecell cup and cell top form the transition between the casing areas andthe top and bottom areas. They are preferably therefore bounded on theone hand by essentially flat bottom and top areas, and on the other handby the essentially cylindrical casing areas, which are arranged at rightangles to them. By way of example, the edge areas may be in the form ofa sharp edge, or else may be rounded.

The procedure for producing a button cell which is not beaded over isgenerally to first of all apply a seal to the casing area of a cell top.In a further step, the cell top is then inserted, with the seal fitted,into a cell cup thus resulting in an area in which the casing areas ofthe cell cup and cell top overlap. The size of the overlap area and theratio of the overlapping area to the non-overlapping areas are in thiscase governed by the respective height of the casing areas of the cellcup and cell top, and by the depth of the insertion. With regard to thecasing area of the cell top, it is preferable for between 20% and 99%,in particular between 30% and 99%, particularly preferably between 50%and 99%, to overlap the casing area of the cell cup (the percentageseach relate to the height of the casing or of the casing area). Beforebeing inserted into the housing cup and/or the housing top, the otherconventional components of a button cell (electrodes, separator,electrolyte and the like) are inserted. After the cell top has beeninserted completely into the cell cup a pressure is exerted on thecasing area of the cell cup, in particular in the area of the cut edge,to seal the housing. In this case, a joined-together housing part shouldas far as possible not be subjected to any loads, or only to very smallloads, in the axial direction. Therefore, the pressure is applied inparticular radially. Apart from the sealing of the housing which hasalready been mentioned the external diameter of the cell housing cantherefore also be calibrated.

It is particularly important for the heights of the casing areas of thecell cup and cell top to be matched to one another such that the cutedge of the cell cup is pressed against the casing area of the cell topby the pressure on the casing area of the cell cup. The heights of thecasing areas are therefore preferably chosen such that it is impossibleto bend the cut edge of the cell cup around inward over the edge area ofthe cell top which has been completely inserted into the cell cup.Correspondingly, the edge of the cell cup is not beaded over the edgearea of the cell top. In consequence, the cell cup of a button cellmanufactured using our method has a casing area with an essentiallyconstant radius in the direction of the cut edge.

In the case of button cells produced using a method such as this, thereis preferably an exclusively force-fitting connection between thehousing components comprising the cell cup, the cell top and the seal.This ensures that the components are therefore held together in apreferred manner, essentially only by static-friction force.

Button cells without any beading over are particularly preferablyproduced using a cell cup which is conical at least in one subarea ofits casing, such that at least its internal diameter increases in thedirection of the cut edge. This makes it considerably easier to insertthe cell top into the cell cup. The dimensions of the cell cup and celltop are preferably matched to one another such that relatively largeopposing forces preferably do not occur until the top has been insertedvirtually completely into the cup. The cone angle in this case ispreferably 10 minutes to 3°, in particular 30 minutes to 1° 30 minutes.

The cell top, which is inserted into the cell cup with the applied seal,is preferably cylindrical, at least in a part of the casing area. Thismay relate in particular to that part of the casing area which overlapsthe conical subarea of the cell cup casing that has been mentioned,after the cell top has been inserted into the cell cup. The casing ofthe cell top, and therefore also the casing area, is particularlypreferably entirely cylindrical. The cell top therefore preferably has aconstant external radius in the casing area. This may relate inparticular to that part which overlaps the conical part of the casingarea of the cell cup after the cell top has been inserted.

When a cell top with a cylindrical casing area is being inserted into acell cup which is conical at least in one subarea of its casing, as hasbeen described above, a gap which is open at the top is generallycreated between the cell cup and the cell top. This gap is generallyclosed again by the pressure on the casing area of the cell cup. Thus,the pressure on the casing area of the cell cup may be chosen such thatthe conical part of the casing area of the cell cup is pushed inwarduntil the inside of the cell cup and the outside of the cell top areessentially at the same distance from one another in the overlappingarea. The resultant button cell has casing areas which are alignedparallel to one another, in particular in the overlapping area.

One important aspect in this case is the choice of the seal whichconnects the cell cup to the cell top. The seal is preferably a plasticseal which connects the cell cup to the cell top. The seal is preferablya plastic seal composed of a thermoplastic.

The plastic seal is particularly preferably a film seal, for example, asis described in already cited DE 196 47 593, in particular a film sealcomposed of a thermoplastic.

Film seals can be produced with a very uniform thickness. When asuitable pressure is applied to the casing area of the cell cup, thisresults in an interference fit, as a consequence of which the buttoncell that has been produced has highly excellent sealingcharacteristics. The use of film seals makes it possible to dispensewith the edge of the cell cup being beaded over without this on theother hand resulting in a need to accept disadvantages in otherimportant characteristics.

It is very particularly preferable to use plastic seals, in particularplastic films, based on polyamide or based on polyether ether ketones inthe present case.

It is preferable for the seal for a cell which is not beaded over tohave an initial thickness in the range of 50 μm to 250 μm, particularlypreferably 70 μm to 150 μm, in particular about 100 μm. The term“initial thickness” is in this case intended to mean the thickness ofthe seal before it is applied to the casing of the cell top. In contrastto this, the term “final thickness” is intended to mean the thickness ofthe seal in the finished cell. It is clear that, at least in theoverlapping area, this generally corresponds to the distance between theinside of the cell cup and the outside of the cell top.

To allow a sufficiently large amount of friction to be produced betweenthe cell cup and the cell top, both the external and internal radii ofthe cup and top should be matched to one another and to the thickness ofthe film seal. This is the only way to create a sufficiently highcontact pressure to hold the two individual parts together. It ispreferable for the parts used in this case for the difference betweenthe external radius of the cell top, which is to be inserted into thecell cup, on the cut edge of the cell top and the smallest internalradius of the cell cup in that part of the casing area which overlapsthe casing area of the cell top to be less than the initial thickness ofthe seal that is used. The difference is particularly preferably 10% to90% of the initial thickness, in particular 30% to 70%, and veryparticularly preferably about 50%.

After the cell top has been inserted into the cell cup, a part of thecasing area of the cell cup can be drawn radially inward. In particular,this relates to that part of the casing area which does not overlap thecasing area of the cell top.

We found that this process of drawing in radially makes it possible toachieve considerably better sealing characteristics. Drawing in the cupcasing results in a radial pressure being exerted on the edge sectionwhich rests on the inner wall of the housing cup and on the sealarranged between the housing top and the housing cup, with the seal inconsequence being compressed in this area.

The drawing-in process can be carried out at the same time as thealready mentioned exertion of pressure on the casing area of the cellcup, although the drawing-in process is preferably carried out in asubsequent, separate step.

Our method of producing a button cell can be used in particular toproduce button cells as have been described above, that is to say buttoncells having a housing with a flat bottom area and a flat top areaparallel to it. It is suitable for producing not only button cells whichare not beaded over, but also for those which are beaded over.

With respect to the preferred examples of the individual components usedin our method (housing parts and dimensions, electrodes, separator andthe like), reference can therefore be made to the above statements andexplanations in their entirety.

In general, the housing is assembled from a metallic cup part (housingcup) and a metallic top part (housing top), with an electrode-separatorassembly with electrodes in the form of a flat layer being inserted intothe housing such that the electrodes are aligned at right angles to theflat bottom area and top area.

As already mentioned, the electrode-separator assembly is preferablyinstalled in the form of a winding, in particular a spiral winding.

In general, our method always comprises the following steps:

-   -   insertion of the winding into the metallic top part, and        insertion of the metallic top part with the winding into a        metallic cup part.    -   The edge of the cup part is then optionally beaded over the edge        of the top part.

When a button cell which is not beaded over is produced, thecorresponding steps as described above are carried out.

Before the housing is closed, the electrodes are normally alsoimpregnated with electrolyte solution.

For the insertion process, the winding is preferably rolled up on awinding mandrel. After or during the insertion process, the windingmandrel can then be removed. If required, the winding core that has beenmentioned above is then inserted. Alternatively, the electrode-separatorassembly can also be wound directly onto a core such as this.

The spiral winding is particularly preferably heat-treated on its endfaces before being installed. In this case, it is at least brieflysubjected to a temperature at which the separator in the winding isthermoplastically deformable. In general, the separator projectssomewhat on the end faces of the winding, and this is itself subject tothe precondition that the electrodes are arranged with the offset withrespect to one another, as described above. The heat treatment allowsthe separator to be shrunk together somewhat, therefore, if required,even exposing the edge of an adjacent electrode, such that this can restdirectly on the button cell housing.

The stated advantages and further advantages will become evident fromthe description which now follows of the drawings. In this case,individual features may be implemented on their own or in combinationwith one another. The described examples are intended only forexplanation and better understanding, and should in no way be understoodas being restrictive.

FIG. 1 schematically illustrates the cross section through one preferredexample of a button cell 100. This has a metallic cup part 101 andmetallic top part 102. The two parts are connected to one another,sealed by a seal 109. Together, they form a housing with a flat bottomarea 103 and a flat top area 104 parallel to it. When in use, these flatareas 103 and 104 form the poles of the button cell, from which currentcan be drawn by a load. The edge 110 of the cell cup 101 is beadedinward over the edge of the cell top 102.

An arrangement comprising an electrode 105 in the form of a strip, anelectrode 106 in the form of a strip, and the separators 107 in the formof strips is arranged in the interior of the electrode. The assemblycomprising the electrodes 105 and 106 as well as the separators 107 isin this case in the form of a winding, whose end faces abut against theflat bottom area 103 and the flat top area 104, which is parallel to it.The assembly is wound up on the core 108 in the center of the buttoncell 100. Both the core 108 as well as the electrodes and separatorswhich are wound around it are aligned at right angles to the flat bottomand top areas 104 and 103. When the volume of the electrodes increasesor decreases during a charging or discharging process, the mechanicalforces which result in this case act predominantly radially, and can beabsorbed by the casing area of the button cell 100.

It should be stressed that the positive electrode 105 and the negativeelectrode 106 respectively rest directly on the cup part 101 and on thetop part 102 of the button cell 100. There is no need for a separateoutput conductor for connecting the electrodes to the top part 102 andto the cup part 101.

FIG. 2 shows the effect of the heat treatment of an electrode-separatorwinding 200, which is provided in preferred examples of the method ofproducing a button cell. The illustration schematically shows a winding200 comprising an assembly of a positive electrode 201 (bar with crossstrips), a negative electrode 202 (white bar) and the separators 203(detail). The positive and the negative electrodes 201 and 202 are ineach case arranged offset with respect to one another. The separators203 are composed of a thermoplastically deformable material.

When the separator edges which are located on the end faces 204 and 205of the winding 200 are subjected to a high temperature (for example, of250° C., as illustrated), then these separator edges shrink. Theseparators are drawn in at least partially between adjacent electrodes.In the process, the edges of the negative electrode 202 are exposed onthe end face 204, while the edges of the positive electrode 201 arecovered. The edges of the positive electrode 201 on the end face 205 areexposed, while the edges of the negative electrode 202 are covered.

When a winding that has been treated in this way is in use, this ensuresthat electrodes of the same polarity can each rest directly only on thehousing cup or on the housing top. There is no need for separateelectrical connections between the electrodes and the housing parts.

FIG. 3 shows an electrode-separator assembly for button cells in theform of a winding 300, with the illustration A depicting a plan viewvertically from above at one of the end faces 301 of the winding 300,while the illustration B shows the winding 300 in a view obliquely fromabove. In both cases, this shows that the assembly comprises two layers;separators 302 and 303 as well as two electrode layers 304 and 305 (apositive and a negative electrode). The assembly is wound up in a spiralshape and is held together by an adhesive tape 306 on its outside.

FIG. 4 shows a sectioned illustration of one preferred example of abutton cell 400. The figure shows the housing of the button cellcomprising the cup part 401 and the top part 402, between which the seal403 is arranged. An assembly of electrodes and separators, as isillustrated in FIG. 3 , is contained as a spiral winding 404(illustrated schematically in the cross section) within the housing. Theseparator layers 405 and 406 as well as the electrodes 407 and 408 ofopposite polarity can also be seen well here. In this case, theelectrode 407 is connected via the output conductor 410 to the top part402, while the electrode 408 is connected via the output conductor 409to the cup part 402. The output conductor 410 is preferably welded tothe top part 402. In contrast, the output conductor 409 is connected tothe cup part 402 via a clamping connection (it is clamped in between thesupporting ring 413, on which the edge of the cell top rests, and thebottom of the cell cup). The insulating means 411 and 412 are arrangedbetween the end faces of the winding and the cup part 401 and the toppart 402, and are each in the form of thin plastic disks. This preventselectrodes of opposite polarity from being able to come into contactwith the cup part 401 or the top part 402 at the same time. Thisprevents any short circuit.

FIG. 5 schematically illustrates the cross section through one preferredexample of a button cell 500.

This button cell 500 has a metallic cup part 501 and a metallic top part502. The two parts are connected to one another, sealed by a seal 510.Together, they form a housing with a flat bottom area 503 and a flat toparea 504 parallel to it. When in use, these flat areas 503 and 504 formthe poles of the button cell, from which current can be drawn by a load.

The cell top 502 is inserted into the cell cup 501 such that the casingareas of the cell top and of the cell cup overlap. When the cell top 502is inserted in the cell cup 501, the cell cup has a conical casing area501′, which is subsequently pushed inward, the internal radius of thecell cup 501 in the overlapping area then being essentially constant inthe direction of the cut edge. Therefore, the edge of the cell cup 501is not beaded over the edge 511 of the cell top 502, and the preferredexample described above for a button cell 500 is therefore a button cellwhich is not beaded over.

An assembly comprising an electrode 508 in the form of a strip, anelectrode 509 in the form of a strip and separators 507 in the form ofstrips is arranged in the interior of the electrode. The assemblycomprising the electrodes 508 and 509 as well as the separators 507 isin this case in the form of a winding, whose end faces face in thedirection of the flat bottom area 503 and of the flat top area 504 whichis parallel to it. The assembly is wound up on the winding core 512 inthe center of the button cell 500. Both the core 512 and the electrodesand separators which are wound around it are aligned at right angles tothe flat bottom and top areas 504 and 503. If the volume of theelectrodes increases or decreases during a charging or dischargingprocess, the mechanical forces which result in this case actpredominantly radially, and can be absorbed by the casing area of thebutton cell 500.

The positive and the negative electrodes make contact with the housinghalf-part comprising the cup and top via the output conductor 505 andthe output conductor 506. The output conductor 505 is composed ofaluminum, and the output conductor 506 is composed of nickel (oralternatively of copper). Both output conductors are thin films, whichrest flat between the end faces of the winding and the flat top andbottom areas 503 and 504. A continuous slight contact pressure ismaintained on the output conductors by the winding core 512. The outputconductors are preferably separated from the end faces of the winding bya separate insulator arrangement 514 (the separate insulator arrangementseparating output conductor 505 from flat bottom area 503 is notillustrated in the drawing), for example, by a thin film.

FIG. 6 shows an electrode-separator assembly for button cells in theform of the winding 300. The assembly comprises two layers; separators302 and 303 as well as two electrode layers 304 and 305 (a positive anda negative electrode). The assembly is wound up in a spiral shape and isheld together by an adhesive tape 306 on its outside. In the embodimentdepicted in FIG. 6 , a first of the electrode layers 304 and 305 isformed from a first metallic film or metallic mesh covered with anelectrode material. The first metallic film or metallic mesh includes anuncovered end piece bent such that a portion 308 of the uncovered endpiece extends out of the electrode-separator assembly winding and atleast partially lies flat on an end face 301 of the electrode-separatorassembly winding 300.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive. Itwill be understood that changes and modifications may be made by thoseof ordinary skill within the scope of the following claims. Inparticular, the present invention covers further embodiments with anycombination of features from different embodiments described above andbelow. Additionally, statements made herein characterizing the inventionrefer to an embodiment of the invention and not necessarily allembodiments.

The terms used in the claims should be construed to have the broadestreasonable interpretation consistent with the foregoing description. Forexample, the use of the article “a” or “the” in introducing an elementshould not be interpreted as being exclusive of a plurality of elements.Likewise, the recitation of “or” should be interpreted as beinginclusive, such that the recitation of “A or B” is not exclusive of “Aand B,” unless it is clear from the context or the foregoing descriptionthat only one of A and B is intended. Further, the recitation of “atleast one of A, B and C” should be interpreted as one or more of a groupof elements consisting of A, B and C, and should not be interpreted asrequiring at least one of each of the listed elements A, B and C,regardless of whether A, B and C are related as categories or otherwise.Moreover, the recitation of “A, B and/or C” or “at least one of A, B orC” should be interpreted as including any singular entity from thelisted elements, e.g., A, any subset from the listed elements, e.g., Aand B, or the entire list of elements A, B and C.

What is claimed is:
 1. A method for producing a button cell, the methodcomprising: providing a cell cup, the cell cup having a flat bottomarea, a cell cup casing, and a bottom edge forming a transition betweenthe flat bottom area and the cell cup casing; providing a cell top, thecell top having a flat top area, a cell top casing having a firstheight, and a top edge forming a transition between the flat top areaand the cell top casing, wherein at least a portion of the cell topcasing is cylindrical; providing an electrode-separator assemblywinding, the electrode-separator assembly winding having: a positiveelectrode formed from a first portion of a first metallic film ormetallic mesh covered with a first electrode material, and a negativeelectrode formed from a first portion of a second metallic film ormetallic mesh covered with a second electrode material, wherein: thefirst portion of the first metallic film or metallic mesh covered withthe first electrode material and the first portion of the secondmetallic film or metallic mesh covered with the second electrodematerial are connected to one another by a separator layer and wound up,along their length, in a spiral shape about an axis, and a respectivemetallic film or metallic mesh includes a second portion, the secondportion being a length of the respective metallic film or metallic meshthat is not covered with the electrode material and that serves as anoutput conductor, the respective metallic film or metallic mesh beingthe first metallic film or metallic mesh or the second metallic film ormetallic mesh; applying an electrically insulating seal at least to anouter portion of the cell top casing; inserting the electrode-separatorassembly winding into the cell top; inserting the cell top into the cellcup to form a housing, wherein: the flat top area is parallel to theflat bottom area, the axis of the electrode-separator assembly windingis aligned at right angles to both the flat top area and the flat bottomarea, the respective metallic film or metallic mesh is bent such thatthe second portion of the respective metallic film or metallic mesh atleast partially lies flat between an end face of the electrode-separatorassembly winding and one of the flat bottom area or the flat top area,and the cell top casing and the cell cup casing form an overlap areaextending in a direction parallel to the axis of the electrode-separatorassembly winding and having a second height, the second height beingbetween 20% and 99% of the first height; and applying, in a radialdirection perpendicular to the axis of the electrode-separator assemblywinding, a pressure on the cell cup casing so as to seal the housing,wherein the portion of the cell top casing that is cylindrical forms atleast a part of the overlap area.
 2. The method of claim 1, wherein theportion of the cell top casing that is cylindrical extends through theentire overlap area in the direction parallel to the axis of theelectrode-separator assembly winding.
 3. The method of claim 1, whereinthe cell top has a constant external radius in an area of the cell topcasing such that the entirety of the cell top casing is cylindrical. 4.The method of claim 1, wherein the cell cup casing has, at an endopposite the bottom edge, a cut edge, and wherein the cell cup casinghas a third height, the third height being less than the first heightsuch that, when the cell top is inserted into the cell cup to form thehousing, it is impossible to bend the cut edge of the cell cup casingover the top edge of the cell top.
 5. The method of claim 1, wherein thecell cup casing has a conical subarea such that an internal diameter ofthe cell cup casing increases in a direction extending away from theflat bottom area, wherein the conical subarea of the cell cup casingfacilitates the inserting the cell top into the cell cup.
 6. The methodof claim 5, wherein the inserting the cell top into the cell cup createsa gap between the cell cup casing and the cell top casing, the gap beingadjacent to the conical subarea of the cell cup casing, and wherein theapplying, in the radial direction, the pressure on the cell cup casingcauses a reduction in a width of the gap.
 7. The method of claim 6,wherein the cell cup casing has, at an end opposite the bottom edge, acut edge, and wherein applying, in the radial direction, the pressure onthe cell cup casing so as to cause a reduction in the width of the gapcomprises applying the pressure in the radial direction to the cut edgeof the cell cup casing.
 8. The method of claim 6, wherein the applying,in the radial direction the pressure on the cell cup casing provides aninterference fit between the cell top and the cell cup.
 9. The method ofclaim 5, wherein the applying the electrically insulating seal at leastto the outer portion of the cell top casing includes applying a firstportion of the electrically insulating seal to the portion of the celltop casing that is cylindrical and forms at least the part of theoverlap area, wherein the first portion of the electrically insulatingseal has an initial thickness prior to being applied to the portion ofthe cell top casing that is cylindrical and forms at least the part ofthe overlap area, and wherein the portion of the cell top casing that iscylindrical and forms at least the part of the overlap area has anexternal radius, wherein the cell cup casing has, in the overlap area, asmallest overlap internal radius, and wherein a difference between theexternal radius and the smallest overlap internal radius is 10% to 90%of the initial thickness.
 10. The method of claim 9, wherein thedifference between the external radius and the smallest overlap internalradius is 30% to 70% of the initial thickness.
 11. The method of claim9, wherein the initial thickness is in the range of 50 μm to 250 μm. 12.The method of claim 1, wherein the applying an electrically insulatingseal at least to an outer portion of the cell top casing includesapplying a first portion of the electrically insulating seal to theportion of the cell top casing that is cylindrical and forms at leastthe part of the overlap area, wherein the first portion of theelectrically insulating seal has an initial thickness prior to beingapplied to the portion of the cell top casing that is cylindrical andforms at least the part of the overlap area, and wherein following theapplying, in the radial direction, the pressure on the cell cup casingso as to seal the housing formed by the cell cup and the cell top, thefirst portion of the electrically insulating seal has a final thicknessthat is less than the initial thickness thereby providing frictionbetween the cell cup and the cell top so as to hold the cell cup and thecell top together.
 13. The method of claim 1, further comprising drawinga part of the cell cup casing radially inward.
 14. The method of claim1, wherein simultaneously to the applying, in a radial directionperpendicular to the axis of the electrode-separator assembly winding,the pressure on the cell cup casing so as to seal the housing, a part ofthe cell cup casing is drawn radially inward.
 15. The method of claim 1,wherein the first electrode material is a lithium-intercalatingelectrode material.
 16. The method of claim 1, further comprising:welding second portion of the respective metallic film or metallic meshto the flat bottom area or the flat top area.
 17. The method of claim 1,wherein a second respective metallic film or metallic mesh includes asecond portion, the second portion being a length of the secondrespective metallic film or metallic mesh that is not covered with thesecond electrode material and that serves as a second output conductor,the second respective metallic film or metallic mesh being the other ofthe first metallic film or metallic mesh and the second metallic film ormetallic mesh, the method further comprising: bending the secondrespective metallic film or metallic mesh such that the second portionof the second respective metallic film or metallic mesh extends out ofthe electrode-separator assembly winding and at least partially liesflat between a second end face of the electrode-separator assemblywinding and another of the flat bottom area or the flat top area. 18.The method of claim 17, further comprising: welding the second portionof the respective metallic film or metallic mesh to the flat bottom areaor the flat top area, and welding the second portion of the secondrespective metallic film or metallic mesh to the other of the flatbottom area and the flat top area.
 19. The method of claim 1, furthercomprising providing an insulator between fi) the end face of theelectrode separator assembly winding and (ii) at least part of thesecond portion of the respective metallic film or metallic mesh that atleast partially lies flat between the end face of theelectrode-separator assembly winding and the one of the flat bottom areaor the flat top area.
 20. The method of claim 19, wherein the insulatorcompletely covers the end face of the electrode-separator assembly. 21.The method of claim 17, further comprising: providing a first insulatorbetween (i) the end face of the electrode separator assembly winding and(ii) at least part of the second portion of the respective metallic filmor mesh that at least partially lies flat between the end face of theelectrode-separator assembly winding and the one of the flat bottom areaor the flat top area, and providing a second insulator between (i) thesecond end face of the electrode-separator assembly winding and (ii) atleast part of the second portion of the second respective metallic filmor metallic mesh that at least partially lies flat between the secondend face of the electrode-separator assembly winding and the another ofthe flat bottom area or the flat top area.
 22. The method of claim 21,wherein the first insulator completely covers the end face of theelectrode-separator assembly winding, and wherein the second insulatorcompletely covers the second end face of the electrode-separatorassembly winding.
 23. The method of claim 1, wherein the positiveelectrode, the negative electrode, and the separator collectively form amulti-layer assembly.
 24. The method of claim 23, wherein providing theelectrode-separator assembly winding includes rolling the multi-layerassembly around a winding mandrel or a winding core.
 25. The method ofclaim 24, further comprising, prior to inserting the cell top into thecell cup, removing the winding mandrel or the winding core from theelectrode-separator assembly winding.
 26. The method of claim 1, whereinthe electrode-separator assembly winding further includes a windingcore.
 27. The method of claim 1, wherein the positive electrode and thenegative electrode are ribbons having thicknesses in the range of 10 μmto 1000 μm.
 28. The method of claim 1, wherein the separator layer is aporous plastic film having a thickness in the range of 3 μm to 100 μm.29. The method of claim 1, wherein the separator layer is a porousplastic film having a thickness in the range of 10 μm to 50 μm.
 30. Amethod for producing a button cell, the method comprising: providing acell cup, the cell cup having a flat bottom area, a cell cup casinghaving a first height, and a bottom edge forming a transition betweenthe flat bottom area and the cell cup casing; providing a cell top, thecell top having a flat top area, a cell top casing having a secondheight, and a top edge forming a transition between the flat top areaand the cell top casing, wherein at least a portion of the cell topcasing is cylindrical; providing an electrode-separator assemblywinding, the electrode-separator assembly winding having: a positiveelectrode formed from a first portion of a first metallic film ormetallic mesh covered with a first electrode material, and a negativeelectrode formed from a first portion of a second metallic film ormetallic mesh covered with a second electrode material, wherein: thefirst portion of the first metallic film or metallic mesh covered withthe first electrode material and the first portion of the secondmetallic film or metallic mesh covered with the second electrodematerial are connected to one another by a separator layer and wound up,along their length, in a spiral shape about an axis, and a respectivemetallic film or metallic mesh includes a second portion, the secondportion being a length of the respective metallic film or metallic meshthat is not covered with electrode material and that serves as an outputconductor, the respective metallic film or metallic mesh being the firstmetallic film or metallic mesh or the second metallic film or metallicmesh; applying an electrically insulating seal at least to an outerportion of the cell top casing; inserting the electrode-separatorassembly winding into the cell top; inserting the cell top into the cellcup to form a housing, wherein: the flat top area is parallel to theflat bottom area, the axis of the electrode-separator assembly windingis aligned at right angles to both the flat top area and the flat bottomarea, the respective metallic film or metallic mesh is bent such thatthe second portion of the first metallic film or metallic mesh at leastpartially lies flat between an end face of the electrode-separatorassembly winding and one of the flat bottom area or the flat top area,and the cell top casing and the cell cup casing form an overlap areaextending in a direction parallel to the axis of the electrode-separatorassembly winding and having a third height, wherein the first and secondheights are related such that the third height is less than secondheight; and applying, in a radial direction perpendicular to the axis ofthe electrode-separator assembly winding, a pressure on the cell cupcasing so as to seal the housing, wherein the portion of the cell topcasing that is cylindrical forms at least a part of the overlap area.